Method and apparatus for coating sheet material



July 18, 1944. L L MCGLADREY ETAL 2,354,033 A METHOD AND APPARATUS FOR COATING SHEET MATERIAL Filed Oct. 15, 1941 4 Sheets-Sheet 1 INVENTOR ATTORNEY y 9 L. L M GLADREY ETAL. 2,354,033

METHOD AND APPARATUS FOR COATING SHEET MATERIAL Filed Oct. 15, 1941 4 Sheets-Sheet 2 Z 111 0 cfflwdw INVENTOR ATTORNEY jZLQ.6

y 1944- L. L. M GLADREY ETAL 2,354,033

METHOD AND APPARATUS FOR GOA TING SHEET MATERIAL Filed Oct. 15, 1941 4 Sheets-Sheet 5 INVENTOR lav/W ATTORNEY July 13, 9 L. 1.. M GLADREY ET AL METHOD AND APPARATUS FOR COATING SHEET MATER IAL Filed Oct. 13, 1941 4 Sheets-Sheet 4 flay/.11

' z lum aw J 9 .M 6 7 w a 4 x ATTORNEY Patented July 18, 1944 2,354,033 7 V Marnon AND srrsas'rus FOR COATING SHEET MATERIAL Lyle L. McGladrey, Minneapolis, and Cecil M..

Rhodes,-St. Paul, Minn., assignors to Rapinwax Paper Company, Minneapolis, Minn, a corporationof Minnesota Application October 13, 1941, Serial No. 414,744.

1 Claims. (Cl. 117-102) Our invention relates to an improvement in coating methods and apparatus for coating paper, or other film materials.

In the coating of paper orcellulose films, such as those used for packaging food and other products, it has-been difllcult to obtain a thin even coating over the paper or film surface. Complicated and expensive equipment has been constructed to regulate the thickness of the coating. Such expensive and complicated mechanism is difilcult to maintain and requires considerable expense to keep in operation. A a result, is has,

in some instances, been most practical to allow the coating thickness to vary tosome extent rather than to use such equipment whichis difiil6 cult to maintain.

The thickness of the coating on paper or other In the first place, a variation in thickness of the coating varies the drying time of the coated sheet. Thus if the machine is set to dry the coating of a certainv thickness, certain portions of the sheet which are lightly coatedmight berdried too great an extentwith a bed effect upon the finished product. Otherparts of the coated sheet may bear a coating of excessive thickness which will not be properly dried during the progress of the sheet, thus producing a product which is not uniform in grade.

To the manufacturer, perhaps the greatest dimculty arises in the expense of thecoating upon the sheet. The sheet is manufactured in certain specifications,-and must meet certain mini- A further diiiiculty has been encountered in providing an even coating, due to slight changes in tension of the paper as it passes through the coating machine. While' constant tension devices are in common use on such machines, it is dimcult to hold the paper against the coating appliance with exactly the sametension at all times so as to insure an even coating. Furthermo e. as most sheets are somewhat bag y. it

dimcult to maintain a-constant tension throughout the widthot the sheet.

11 The objector our invention is to eliminate forl gmer di-iiiculties with devices of this nature by pro- ?viding ameans of applying the coating to the paper and by passing the coated surface over a acuum chamber which draws the paper against suitable doctor blade with constant pressure.

@Tlihua, as the coating passes over the blade, it is {drawn against the blade with a constant pres- 20L isure and. scrapes or removes from this. sheet of uniform thickness upon the sheet. We have .-'found that such a device may be used to replace metering mechanism which is extremely fcostly and expensive to maintain, and we have fobtained more uniform results than with such prior devices. As a result, our apparatus will coat the sheet with a more uniform coating than has been previously possible.

"A purpose of our invention lies zin the provision or a sheet coating apparatuswhichincludes an apparatus for applying the coating to the surface of the sheet. A vacuum chamber is then provided over which the sheet travels,- and the sheet is as drawn into this vacuum chamber to a predeterwhich defines one edge of the vacuum chamber with a p redetermined pressure which does not o vary tofblhy appreciable degree during the movemum requirements. For example, if theiizfsheet' is to be coated to render the sheet more moistureproof, the coating must be of a certain minimum thickness to produce the proper degree of moistureprgofness. If the coating is irregularly-apment of the paper. As a result, the uniform pres sure of the paper on the doctor blade acts to remove all but a predetermined thickness of coatplied, andis thicker at some points than at others,

the coating must have the necessary minimum thickness to meet the necessary specifications ever itsentire area. As a result, parts of the sheetare coated-much more heavily than is required to meet the specifications, thus considerably increasing the cost. As the coatings are often ex-' tremely costly an even coating thickness is of great importance to themanuiacturer.

ing from the paper, resulting in a uniform coatingover the entire sheet. This vacuum chamber holds the sheet in place with a constant force regardless of the fact that the sheet may be baggy at some points.

A feature of our invention resides in the fact that the coatingthickness corresponds to the amount of vacuum applied. There is a definite relation between the vacuum in the chamber as measured by a gauge and the coating thickness. Thus the coating thickness (temperature and vis- Jl cosity remaining constant) may be measured by ;the excess coating material so as to leave a film a vacuum gauge in communication with the vacuum chamber.

A feature of our invention resides in the fact that the doctor blade may be positioned on either side of the vacuum chamber so as to either remove the excess coating material before the paper travels over the vacuum chamber, or else to remove the coating with the air leaking into the vacuum chamber. If this latter arrangement is used. a means for separating the excess coating from the air pumped by the vacuum pump is necessary.

A feature of our invention resides in the provision of a coating machine in which the continuous sheet is drawn with a predetermined pressure against a means for removing an excess coating from the sheet and also provides a predetermined angularity between the sheet and the coating removing means. As the sheet travels over the vacuum chamber, the sheet is bowed into the vacuum chamber, thus flexing the paper out of its normal path and deflecting the paper to a predetermined degree. Thus the angle be tween the paper and the coating removing means. which defines one edge of the vacuum chamber remains constant when the amount of vacuum and the tension 01 the sheet remains substantially constant.

A further feature of our invention resides in a novel means of sealing the ends of the vacuum chamber so as to permit the threading of the paper through the machine in a minimum of time, and at the same time sealing the ends of the vacuum chamber with respect to the side edges of the sheet. As coating machines of this type are ordinarily required to coat sheets of varying widths, it is necessary that the sealing means and the edges of the sheet be adjustable to seal the edges of sheets of varying widths. This sealing means is designed to accommodate for the bow or curve in the paper caused by air pressure as the sheet travels over the vacuum chamber.

These and other objects and novel features of our invention will be more clearly and fully set forth in the following specification and claims.

In the drawings forming a part of our specification:

Flgure l is a diagrammatic side view of the coating machine for coating 9. continuous sheet of material, such as paper, or the like.

Figure 2 is a rear view of the coating device illustrated in Figure 1.

Figure Sis-msectional view through the coating head illustrating the construction thereof.

Figure 4 is an el ation view of one of the sheet sealing members for sealing the ends of the vacuum chamber.

Figure 5 is a side elevation view of the sealing element illustrated in Figure 4.

Figure 6 is a sectional view through the coating head, the position of the section being in dicated by the line 0-! of Figure 3.

Figure "I is a sectional view through a modified form of coating head in which the xcess coating removed from the sheet is exhausted simultaneously with the air leaking into the vacuum chamber.

Figure 8 is a front elevation view of the end seal and the paper sheet for the ends of the vacuum chamber.

Figure 9 is a side elevation view of the vacuum chamber end seal illustrated in Figure 8.

Figure 10 is a perspective view sectionally through the coating head showing a portion of a strip of paper being fed therethrough.

Figure 11 is a perspective view of an end seal and the coating chamber over which the sheet must pass.

The coating machine A is provided with a support for the shaft ll of a sheet supply roll II. From the supply roll H the paper travels to the flexibly mounted roll l2. This roll I! is connected by linkage to a brake l3 encircling the shaft ill of the supply roll II. Thus a constant tension device is provided so that when tension ing head, which is indicated in general by the letter B. The coating head B, in the machine illustrated, is pivotally mounted to rotate about a shaft I6 so that the angle which the sheet assumes between the various portions of the coating head and the roller I! and the roller I! may be adjusted. The shaft It supports a pair of brackets 19 on which the coating head is mounted.

The roller 11 is mounted upon a pair of arms 20 which support the shaft II of the roller l1, and which are supported on pivots I! on the side frame members 23. Thus the roll I! may be pivoted from the position shown in full lines in Figure l of the drawings,to the position illus- The sheet Cmay travel over rolls 2!, It, and 21 to the receiving roll 29, which is supported on the frame 10 of the rewind machine D. These rolls 26', "gand 21 may be arranged to heat or to cool the paper, allowing certain coatings to be chilled, if desired, and permitting other coatings to be maintained in a heated condition for drying or setting of volatile materials, or for polymerizing the coatings, if it is desired.

With special reference to the coating head 11- lustrated in Figure 3 of th drawings, it will be noted that an I beam 3| extends transversely of the machine supported by the brackets IS. The I beam 3| includes a central web 32 and end flanges 33 and 34. Secured to the end flanges I3 we provide a roller 35 which may, if desired, contain a preheating liquid, so as to preheat the paper or sheet C, as it travels over the roller 35. Mounted upon th upper surface of the central web portion 32 of the I beam 1, we provide a series of spacer blocks 38 which support the transversely extending bar 31. Mounted upon the bar 31, we provide a cross bar or channel 39 which is closed terial is forced through the supply tubes 43 by any suitabl means, such as pumps, and is forced against the surface of the sheet passing over the bar or channel 39.

Recessed into the upperedge of the cross bar.

or channel 39, we provide a pair of spaced'rods 44 and 45. These rods form a rounded surface over which the sheet C passes, and define the edges ofthe coating chamber. Obviously, the coating from the slot v4i] will fill the space between the rods 44 and 45 within the sheet C when the machine is in operation.

Inorder to fill the ends of the coating compartment, we provide an end sealing means which includes an end block 46 which closes each end of the slot 40 and which is shaped similarly to the slots. In Figure 11 of the drawings the end' block 46 is illustrated in detail. As illustrated 'in this figure, the.body 41 of the block fits within the larger portion of the slot between the lips 4|. In combination with each end block 46, we provide a complementarysealing block 50 which fits between the bars 44 and 45, and which engages the top face of th narrower strip. 49 of.

the end block 46. .The block 50 is provided with rounded edges to closely fit the bars 44 and 46, and is provided with a projecting lip 52 which extends beneath the extreme edge of the sheet C. This means, of course, that the extreme edge of the sheet, is ordinarily not coated by the coat ing material, which is actually desirable in most instances, as the edges of the sheet are ordinarily trimmed, and as in' some instances the uncoated edge of the sheet is preferable; Obviously the lip 52 could extendover the surface of the sheet C, if it were desired, to coat the paper'to its extreme width, but such a construction would have the obvious disadvantage of requiring adjustment of theend blocks after the. paper sheet was in place. I

The complementary block 50 is provided with an aperture 53 extending therethrough, which is aligned with an aperture 54 in the block 46. The

aperture 54 is threaded to engage the end of a:

bolt passing through the aperture 53, so that the two portions of the block may be secured together when a bolt extending through the aper- T tur 53 and into the threaded. aperture 54 is tightened the two portions ofthe end block are clamped together and held from longitudinal movement in the slot 40. This bolt is indicated through the inlet tube 43 to the coating head.

The'side 65 of the channel v56 opposite to the side of the channel supporting the doctor blade 62 is provided-with an inset bar over which the sheet Omay pass. The space within the channel is held under reduced pressure anda pipe 61 is connected to the exhaust pump 55, which acts to exhaust air from the inside of the channel. A separator ID permits separation of any coating which might enter the exhaust chamber from the air exhausted fromwithin the channel. i

In order to form end seals for the vacuum chamber, we provide end blocks H which are designed to rest in the channel and to close the ends of the channel to confinethe exhaust area to the space directly "beneath the sheet 0.. The

endblocks H are each provided with a lower end 11 or reduced widthato fit snugly within the channel 56; and is shaped to lit the channel'sides of coating supply so that it may again be red,

between the edges of the papersheet c. In other,

words, the end blocks. II each form awall defining the end of the vacuum chamber and sealin Figure 3 of the drawings by the numeral 56.

Th manner in which the end blocks and may be adjusted to fit the width of the sheet C is "believed .obvious from the foregoing expla-,

nation. 7 7

'Secured to the central web 32 of the I beam 3!, we provide a channel- 56 which extends longitudinally of the I beam 3| and transversely of the coating'head. One edge of the channel .56

is tapered as indicated by the numeral 51, and a bar 59 is secured to the channel 56by means of the bolt 60, The bar 531s provided with an oppositely tapered edge 6| which, together withing the'space between the sheet and. the channel.

In order that the sheet may be easily positioned in' its proper place over the coating head-, the

end blocks'll are each provided with a projecting block 13 which is connected to the inner edge of the block H by means of a hinge 14. The block 13 is curved along its lower edge 15, and. the curvature of the lower surface .15 agrees with the curvature of the paper between the'doctor blade 62 and the rod 66 when the coating head is in operation. A light flexible blade 16 is clamped between the arcuated surface 16 of the block I8... .and an arcuated clamping block II which is bolted to the block 13. An eccentric 15 engages the top of the block 13, to hold this block in position .with the flexible blade I6 overlying the edge of the sheet C. The eccentric I5 is secured 7 upon ,a shaft 4. which extends through the block II. A collar I! is mounted on the opposite end of the rod 64, and a handle I! is secured into the collar 52. "Bymovement of the handle 33 the eccentric llgrnay be pivoted :irom operative position, illustratedin Figures 4 and 5 of the drawings, ,to an inoperative position in which the eccentric II is released from the block I! so as to allow'this block and the blade 16, supported thereby, to pivot out of operative position.

An aperture 54 extends into the block II and communicates with a vertically extending apere ture 66 which is provided with a needle valve 36;

By adjustment of the needle valve 86, air may be bled into the vacuum chamber when it is found necessary or desirable. Passages 81 extend through the channel .66,

providing channels through which heated or cooled liquid mayflow. Thus if the coatingwis v I of the hot melt type, the channel and the' parts attachedthereto may bemaintained at the proper temperature for keeping .thiscoating ina .j". i molten condition; Steam may provide this heati v ing fluid. or if necessary a cooling medium mag-:1. be employed for certain other types of coating. 5 5

The operation 01' the coating head thus de scribed is believed obvious from the foregoing. description. The coating'is applied to the under surface of the sheet C, while the sheet is between .ilge rods 44 and, and between the end blocks vided' with an excess of coating which is somewhat smoothed by the bar or rod 45 and the excessed coating is scraped oif by the doctor The paper or other sheet material is problade 02, this coating running down through the drain opening 63 through the return-channel or duct 64. The sheet C is held against the doctor blade 62 with a constant pressure which is produced by vacuum, the vacuumpump 69 providing the source of reduced pressure within the channel 56. After the excess coating has been removed, the sheet passes over the rod 66 which may form a smoothing means'for the remaining coating on the sheet C.

In Figures '7 through 11 of the drawings, we disclose a modified form of device in which the coating is removed within the vacuum chamber. In this form of construction the coating head D is supported by a channel 89 to which isbolted, or otherwise secured, an inner channel 90. The channel 90 is provided with an inverted substantially T-shaped slot 9I which is defined by a pair of overhanging lips 92 which define the center or open portion of the slot. A supply pipe 93 is provided for introduction of the coating material into the slot 9|, and end blocks 94 provided with complementary end blocks 95, clamp together by clamping bolts 96, are used to seal the ends of the coating chamber. The blocks 94 and 95 are identical with the blocks 46 and 50, illustrated in Figure 11 of the drawings. Thus the paper sheet C is coated with the mechanism illustrated in Figure '7 in the same manner in which the coating has been previously described.

One edge 91 of the channel 99, which supports the inner channel 90 is tapered, as illustrated at I00. A pair of clamping bars IOI and I02 which are held to the end of the channel 89 by clamping bolts I03 support a doctor blade I04 therebetween. End blocks I05 form the ends of the vacuum chamber and seal the vacuum chamber with respect to the sheet C. The endblocks I06 are formed as clearly illustrated in Figures 8 and 9 of the drawings.

A block I06 projects inwardly from each block I06 and is secured thereto by means of a hinge I01. A flexible blade I09 is clamped between the'lower arcuated surface N of the block I06 and the arcuated clamping plate III which is secured to the block I06 by bolts H2, or other suitable means. The flexible blade I09 is designed to rest upon the surface of the sheet C passing over the coating head.

The block I06 is urged against the paper by means of an eccentric I I3 which is mounted upon a shaft II4. A collar H is mounted on the block I05 on the side of the block opposite to the eccentric H3 and a handle I I6 provides a means of adjusting the eccentric II3. When the handle I I 6 is in the position illustrated in Figure 7 of the drawings, the flexible blade I09 is in engagement with the upper surface of the sheet C, while when the handle H6 is rotated into the position illustrated in Figures 8 and 9, the eccentric H3 is removed from engagement with the block I06, permitting this block to pivot upwardly so as to permit the blades I09 to be pivoted away from the upper surface of the paper for threading purposes and the like. 7

A passage H1 is provided in the block I05 which communicates with a vertical passage II9 extending through the block in which is positioned a needle valve I20. The needle valve I permits air to be bled into the vacuum chamber between the channel side 91 and the clamping bar IOI when it is deemed necessary or advisable. A roller I2I is provided over which the sheet C sary, and if desired a heating or cooling fluid may pass through the roller I22 to accomplish its desired purpose.

The operation of the coating head D is somewhat similar to the operation of the coating head previously described. The sheet C passes over the rods I23 and I24 between the end blocks 94 and 95 and is coated with a coating which is supplied through the supply tube 93. The sheet with an excess of coating passes over the rod I24 and over the doctor blade I04. Between the rod I24 and the doctor blade I04, the paper bows downwardly, being drawn in this direction by suction which is created by the suction pump 69, or by other suitable means. The excess coatin is removed by the doctor blade I 04 and is removed together with air leaking into the vacuum chamber through the passage I25, the coating and air passing through the channel I26 and through suitable communicating pipes to the separating chamber 10 which separates the coating from the air. The coating is then recirculated, if desired, to the supply pipe 93 and again used.

A scraper blade I21 is held by clamping jaws I29 and I30 in communication with the roller I22 to maintain a smooth surface on the smoothing roller I22. The finished paper is found to have an even coating and a continuous coating after passing by the coating head.

In accordance with the patent statutes, we have described the principles of construction and operation of our method and apparatus for coating paper, and while we have endeavored to set forth the best embodiments thereof, we desire to have it understood that obvious changes may be made within the scope of the following claims, without departing from the spirit of our invention.

We claim:

1. The method of coating. a sheet through the use of a coating machine, the method consisting in applying an excessive surface of coating to the sheet, passing the coated sheet over a vacuum chamber with the coated surface subjected to vacuum, this vacuum chamber drawing the coated surface of the sheet against the edges of the vacuum chamber and thereby removing the excess coating.

2. An apparatus for coating a sheet consisting in means for applying a coating to the sheet, a doctor blade, and vacuum means for drawing the sheet against the doctor blade and removing a portion of the coating.

3. An apparatus for coating sheets consisting in means for applying coating to a surface of the sheet, a doctor blade, and a vacuum chamber adjacent said doctor blade, said vacuum chamber drawing said sheet against said docto blade to remove excess coating.

4. A sheet coating device comprising a means for applying coating to a surface of the sheet, a doctor blade, a vacuum chamber adjacent'said doctor blade, means for sealing said sheet with respect to said vacuum chamber, said vacuum chamber acting to draw said sheet against said doctor blade with a predetermined pressure.

5. A sheet coating device comprising a means for applying a coating to the surface of the sheet, a vacuum chamber, means for drawing the coated sheet over said vacuum chamber, and means against which said sheet is drawn 'by suction for removing excess coating.

6. A coating machine comprising a means for applying coating to the sheet, a vacuum chamber over which the sheet is operated, and means interposed between said vacuum chamber and said coating means for removing excess coating, said vacuum chamber drawing said sheet against said coating removing means.

7. A coating apparatus for a moving sheet, comprising a means for applying coating to one surface of said sheet, a vacuum chamber over which said coated sheet extends with said one surface of said sheet directly subjected to partial vacuum, and doctor blade means interposed between said vacuum chamber and said coating means for removing excess coating.

8. A coating device for a continuous sheet-comprising a, means for applying coating to a surface of the sheet, a vacuum chamber past which the coated sheet extends with said coated surface directly subjected to partial vacuum, and doctor blade means adjacent said vacuum chamber to remove excess coating from said sheet and to permit said excess coating to drain into said vacuum chamber, said sheet being drawn against said doctor blade by action of said vacuum chamber.

9. A coating machine comprising a means for applying coating to a sheet, a vacuum chamber past which said sheet extends, coating removing means adjacent said vacuum chamber against which said sheet is urged by vacuum in said vacuum means, and flexible sealing means sealing the edges of said sheet with respect to said vacuum chamber.

10. A coating machine comprising a coating applying means, a vacuum chamber adjacent said coating applying means, coating removing means adjacent said vacuum chamber against which said paper is drawn byaction of said vacuum chamber, and means securing the ends of said vacuum chamber with respect to the edges of said sheet.

11. A coating device for a. continuous sheet comprising a coating applying means, a channel past which the coated sheet extends, a source of vacuum supply to the interior of said channel, a coating removing means adjacent said channel against which the sheet is drawn by vacuum in said channel.

12. A coating machine for a continuous sheet including a means for applying coating to said sheet, a channel past which said sheet extends, a source of supply of vacuum to said channel, coating removing means against which said sheet is drawn by vacuum in said channel, and sealing meansfor sealing said channel with respect to the edges 01' said sheet.

13. A coating machine comprising a means for applying coating to the surface of a sheet, a channel past which the coating sheet extends, a coating removing means against which said sheet is drawn by vacuum in said channel, a source of supply '01 vacuum for said channel, and sealing means adjustable in said channel for sealing the edges or said sheet with respect to said channel.

14. A coating machine comprising a means for applying coating to the surface of a. sheet, a channel past which said sheet is moved after coating, 9. source of supply of vacuum to said channel, a coating removing means adjacent said channel against which said sheet is drawn by vacuum in'said channel, sealing means movable in said channel defining the ends 01 the vacuum chamber within said channel, and flexible means on said sealing means engageable with the opposed edges of said sheet.

LYLE L. McGlLlADREY. CECIL M. RHODES. 

